Examples of the cutting tool generally used for cutting metal materials and the like include those that a cutting insert having a cutting edge is mounted thereon. For example, Patent Document 1 describes a predetermined cutting insert, and a cutting tool with the cutting insert mounted thereon (specifically, an end mill).
FIG. 16(a) is a side view showing the related art cutting tool as described in Patent Document 1. FIG. 16(b) is an enlarged side view showing the related art cutting insert mounted on the cutting tool of FIG. 16(a). As shown in FIG. 16(a), a cutting tool 100 as being the end mill is constructed of a cutting insert 101 comprising a cutting edge, and a holder 111 comprising at the tip end thereof a cutting insert pocket 110 for mounting the cutting insert 101. The cutting using the cutting insert 101 is carried out by rotating the holder 111 around an axis 112 of the holder 111.
As shown in FIG. 16(b), the cutting insert 101 has a cutting edge at the ridge between an upper surface 102 and a side surface 103. The cutting edge comprises a high-positioned corner cutting edge 104, a flat cutting edge 105 having substantially the same height as the high-positioned corner cutting edge 104, and a tilted cutting edge 107 having a height gradually decreasing from the high-positioned corner cutting edge 104 toward the low-positioned corner portion 106.
However, the cutting insert 101 thus constructed is subjected to a large cutting force during cutting. Hence, there is the problem that vibration is likely to occur during the cutting, and the cutting edge is susceptible to chipping. This may become a particularly serious problem in heavy cutting.    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-148424